1. Field of the Invention
This invention pertains to the related fields of computer aided design (CAD) and computer graphics. More specifically, this invention relates to an improved system for mapping surface texture onto a computer rendered image of a three-dimensional object.
2. Background Description
One of the objectives of computer aided design systems is the realistic rendering of an image of a three-dimensional object. By imparting greater realism to computer generated images, a designer is better able to visualize the three-dimensional structure and appearance of an object without actually constructing a physical prototype. One technique for enhancing the realism of a computer generated image is the application of surface "texture" onto the image. In this context, "texture" refers to local surface detail that may comprise surface roughness, graphic patterns and the like.
Various techniques for texture mapping are well known in the field of computer graphics. In "Computer Display of Curved Surfaces", Proceedings of IEEE Conference on Computer Graphics, Pattern Recognition and Data Structure, May 1975, pp. 11-17, Edwin Catmull described a technique for modelling a three-dimensional surface using bicubic patches. The patches are recursively subdivided until no subpatch contains more than a single display pixel. The subpatch is then approximated as a quadrilateral, allowing a simple linear transformation to be used for mapping from texture coordinates to image coordinates. Extensions of Catmull's basic technique were described by James F. Blinn and Martin E. Newell in "Texture and Reflection in Computer Generated Images", Communications of the ACM, October 1976, pp. 542-547.
A field in which visualization of objects with applied surface texture is particularly important is fashion design. A number of systems have been developed that allow a fashion designer to apply different fabric textures and patterns onto a computer generated image of a garment. Such systems permit the designer to visualize a garment made from the selected fabric in a realistic manner, including the distortions naturally introduced by the drapes and folds of fabric as it would appear on an actual three-dimensional garment. A system of this type is described in U.S. Pat. No. 4,888,713 issued to Falk. In this particular system, an operator applies an orthogonal mesh to an image of a garment and, using a variety of CAD tools, distorts the mesh so that the mesh appears to have the proper perspective, including wrinkles and folds of the fabric. Texture is then applied using conventional mapping techniques such as described in the above-referenced articles. Such a system produces acceptable results, but requires substantial operator time to make all the necessary adjustments to the mesh so that a realistic image results. Furthermore, the system operates strictly in two dimensions so that no information about the three-dimensional topology of the object is derived. Consequently, the system described by Falk cannot be used to alter the illumination and shadowing of a garment or its orientation with respect to the operator.
The present invention provides an improved method for adding surface texture to a two-dimensional image of a three-dimensional object such that operator time is substantially decreased and such that the object is mathematically modelled in three dimensions.